Ditko's original cover, being more obviously set in daylight, makes the point even better.

This has not stopped people asking me, with perfectly straight faces, why no one can tell Superman and Clark are the same guy since they both have blue hair!

Many characters have begun their careers not only with black costumes, or costume parts, but with outfits that had much more detail than subsequent versions. Ditko's early Spider-Man was red and black, and the red parts were thick with webbing. As the book continued, and deadline pressures began to crowd him, tho, Ditko (perhaps unconsciously) began simplifying the web pattern and leaving the black parts more and more open for color.

Same thing happened to Batman. Originally in a black cape and cowl, with black boots and trunks, it did not take long at all for them to "turn blue". Ditto for the X-Men's school uniforms. Ditto for their "graduation" costumes.

Another factor besides deadlines worked into this. Many artists did for "full pencils" what would today be called breakdowns. They put in all the line work, but they left it for the inker to spot blacks. If they didn't -- well, suddenly the FF no longer had black collars and circles around their chest emblems. (This also affected a lot of Kirby's costume designs. He would often draw the character fully detailed only in the first shot, and leave it for the inker to carry thru with the details in the rest of the issue or appearance. Check Magneto's first appearance, or the Destroyer.)

Curiously, some characters went the other way. Daredevil, for instance, started with a red costume, with little shading, but from time to time, depending on the artist, it would look more like a black costume with red highlights.

Of course, nothing will ever explain to me how anyone in his right mind could look at this costume...